Practice English Speaking&Listening with: LEC 1

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hello this is an introductory course on circuits and systems or networks and systems

suitable for an under graduated students major in electrical engineering with either to power

or communication option in this course we will study the dynamic

behavior of systems and networks you will be expose to a

variety of tools and techniques which are used to study the behavior of the systems

under with the dynamic inputs so that you can gain an or what particular

techniques to choose under a given situation when talking about systems we should also

talk about signals the input variables to a system the response

variable that where looking for and the various intermediate variables which occur a different

points in the system are all collectively called signals

and this is the term which we will use to describe this

variables associated with systems later on we will say that a network is a special kind

of systems and the voltage and current variables associate

with a circuit or a network therefore are also called signals

in the particular contest of a electrical work these signals are usually functions of

time a study of the characteristic of the signals and there

analysis therefore it an integral component of our course

as a matter of fact it is the interplay between the signals and systems that will be the main

theme or and focus of our course among the topics which

will study or for your methods for your transform laplace transform method network functions

and network theorems z transform methods and state variable

techniques these will be the various topics that will be broadly covered under this course

we shall for the most part confine ourselves largely

to the discussion of linear time invariant systems the

meaning of these 2 adjectives linear and time invariant will become clear as we go along

suppose is to say that the form a large class of useful systems so at

the end of this course you will have with you a tool kit of available

techniques so that you can choose 1of these took techniques for the solution of with a

dynamic behavior of a network and system belonging to this very

large class of linear time invariant systems before a proceed

before we proceed further to discuss the meaning of a system let me first talk about the various

text books and reference books that we may like to refer

to during the your study of the material under this course

you may use this book to have some of your doubts clarify to deepened your understanding

of a particular topic may be to get additional information

related to some of the topics that are discussed here but most

importantly you should this book for working out the various problems and answering the

various questions that are given as exercises in this book particularly

for a subject with an analytic analytic orientation like network and systems it is very important

that you should work out a large number of this quantitative problems and answer this

various questions it is only through such exercises that you

can from your understanding with the subject make your grip

of the various techniques stronger and another important aspect with this is that like an

any other discipline in network and systems also there

will be always a number of approaches to solve a

particular problem only through working out to this various exercises you will be having

the ability to choose a the most direct method of attack

for any 1problem you have necessary expertise to gain the

insight so that you can select the most appropriate method of attack for the solution of a problem

and not only that to carry out the solution correctly

and in quick time so i would once again emphasize the importance of working out a variety of

problems and you can use some of the text books which

i am going to mention right now ah as a source material for this problems now the

particular text books that i would like to recommend are hayt and kemmerly engineering

circuit and analysis van valkenburg network analysis

these 2are very popular books in this field openheim willksy and young signals and systems

is a very comprehensive gives a very comprehensive coverage of the topic that are covered in

this course thats an additional topics and this also

contains a wealth of problems and exercises in addition to these 3 books you

have a book by cheng titled analysis of linear systems liu and liu linear systems analysis

and a sixth book by aatre network theory and filter

design it contains discussion of some other topics we are going to cover in this course

like state variable methods and so on which are

not perhaps found in some of the other books by way of a background i expect of you to

follow this course let me mention that ah i expect

the students to have a background on the following topics i assumed that you had a basic course

in electrical circuit analysis which includes the discussion of the properties

of various circuits elements dc and ac circuits analysis ac circuit analysis on the study

state sinusoidal conditions and an idea of elementary

transients time constants and rc circuit rl circuit and so on and setting up the differential

equation pertaining to simple circuits this is a background in electrical engineering

that 1you have as per mathematics systems and you should

be familiar with elements of differential and integral calculus solution of simple linear

differential equations ordinary differential equations a constant coefficient you should

also have an idea of matrices and determinants solution of linear algebraic equations and

then elements of complex variable theory is also

expected a few to follow this course so this is the background what 1would expect you to

have follow this course now let us discuss what

a system means all of us have an idea what a

system is constituted of through its usage in every day terminology we may formally say

a system is a collection of components put together

to serve a particular purpose these components are

are system components that are unified through some kind of int inter dependence among

them they react with each other so that the whole system function as a whole to serve

a particular purpose you may think of a power system the

national educational system hospital systems railway

systems transportation systems and so on and so forth many of these systems also have as

a integral component the interaction of people for example

in social economic system all these are constituents of systems now therefore a system is a collection

of objects united through some form of interdependence among the various components or sub systems

as you may call now the variables that describe the status of

this various components and a system may be quite diverse depending upon the nature of

the component the nature of the system and so and so forth for

example if you are talking about an electro mechanical

system you may have the electrical variables voltage and current associate with a electrical

components and mechanical variables like force and velocity

which describe the status of the mechanical components

at the particular point of in the system at a particular point in the system therefore

system is a_ concept which includes the whole variety of

ah situations that once comes across now what about a network

literally speaking a network is a structure which resembles a kind of net but in our particular

contest the term network to describe a system in which

all the components are of a related kind that means the

variables which are of importance in this system are all of the same kind so in a particular

electrical network for example is a special kind of a

system in which the variables are voltages and currents most

often that is these are the 2variables which are the interest towards the electrical network

similarly we can have a network representing a mechanical

system which will call a mechanical network we use the

variables may be velocities and then force and so on and so forth so we can think of

a net network as a special kind of a system in electrical network

in particular is what constitutes the focus of our

discussion here now we analyzing these systems and networks the first up usually is to model

the system in terms of idealized components put together

in a particular fashion this evolution of the model is

d1with 2conflicting requirements in our mind what are the 2conflicting requirements first

of all we should like to have the model as realistic

as possible so that it stimulates the real system in other

words we should like to make the model as complex as possible so that we loose as little

information about the system as possible on the other

hand we should also like to make the model as simple as possible

to lend itself to convenient mathematical analysis so that the person uses this model

for analysis and synthesis we retain a sanity in a sense because

if it is going to be a huge a complex type of model

we will be never to able solve it therefore these are the 2conflicting requirements in

the evolution of a model of a given physical system the on

1hand it should be as complex as possible so that it will

loose as little information about the system as possible at the same time it has got to

be simple enough to be lend itself to convenient mathematical

analysis now we are very often refer to the model itself

as a system even though we must always keep at the back of our mind that the model is

a mathematical representation is an idealized representation

the physi the actual physical system is something different

and some in some ways a physical system may not the characteristic may not agree with

a model and if it so then we have to the find the model to make

it more realistic where ever it is warranted now in arri

in arriving at a model for a particular system the derivation of the model is specific to

the particular discipline you must study the situation you

must know the characteristic of these and arrive a

suitable model but once we have evolved a model then a whole lot of the system can be

analyses through a common frame work a common set of mathematical

tools which can be used to analyze a whole lot of this

different system system models because the mathematical equations that govern the operation

of the various system are more or less the same therefore

there is a unifying body of techniques and knowledge which

come under the general title system theory at principle of the system analysis which

will be the main scope of our study in under this course

The Description of LEC 1